Method and means for demagnetizing



M. L. MAGES METHOD AND MEANS FOR DEMAGNETIZING April 2, 1946.

2 Sheets-Sheet 1 Filed Aug. 13, 1943 10 z m my 5/ w 1 0 Win m u 7. w Wfl. v

r mkwmz a ma 4/9 nv v at W v v\/ v y Patented Apr. 2, 1946 METHOD ANDMEANS ron DEMAGNETIZING Morris L. Mages, Chicago, Ill., assignor toMagnaflux Corporation, Chicago, Ill., a corporation of DelawareApplication August 13, 1943, Serial No; 498,524

Claims.

This invention relates to a method and means for demagnetizing and moreparticularly to a novel method and means for demagnetization with theuse of transients.

Some of the troublesome problems encountered in the field are thedemagnetization of large parts, in particular, crankshafts, or smallerparts of highly retentive material such as heavy springs. It is quitecommon today for manufacturers to test metal parts for flaws and otherdefects by magnetizing the part and then depositing paramagnetic powderon the part for the purpose of observing any special congregation ofparticles as would be the case if a flaw or other defect were present inthe metal. It is usually considered desirable and in many cases it isabsolutely necessar that a part which has been tested in such a mannerbe demagnetized after the test. Where a crankshaft or other large orspecial part has been magnetized, it is not always possible to obtainsatisfactory demagnetization of the part by simply drawing the partthrough and out of an alternating magnetic field.'

I have found that a very satisfactory demagnetization of a part may beobtained by utilizing the starting transient when a demagnetizing coil15 first connected to an alternating current power line. Moreparticularly, I have found that if a rapid and successive series oftransients is first to the time when a steady alternating current iscaused to flow through the coil so as to enable the part to be graduallywithdrawn from the influence of the field, that a much more satisfactorydemagnetization will result.

It is an object of the present invention to provide a novel method andmeans for demagnetizing which includes the use of transients.

Another object of the present invention is to provide a noveldemagnetizing apparatus wherein the alternating current energizationcircuit of the invention is to provide a novel timer control circuit fordemagnetizing equipment.

The novel features which I believe to be characteristic of my inventionare set forth with Darticularity in the appended claims. My inventionitself, however, both as to its manner of construction and method ofoperation, together with further objects and advantages thereof, maybest be understood by reference to the following description, taken inconnection with the accompanying drawings, in which: v

Figure 1 is a schematic wiring diagram of the novel control circuit fora demagnetizer embodying thenovel principles and teachings of thepresent invention; T

Figure 2 illustrates in full lines the steady state voltage and currentflowing in the demagnetizing coil while the transient is shown in dottedlines;

Figure 3 shows the nature of the resulting curve when the transient iscombined with the steady current;

Figure 4 is a hysteresis curve showing the effect of the transient onthe magnetization of the part being tested; 7

Figure 5 is a schematic wiring diagram illustrating a modified form ofthe present invention;

' and I introduced into the demagnetizing coil prior to demagnetizer isturned on and off a number of rapidly interrupting the flow ofalternating cur-= rent to the energization circuit of the demagnetizer.

Another and still further object of the present Figure 6 is a schematicwiring diagram illustrating a third embodiment of the Present invention.

One embodiment of the present invention is illustrated in Figure 1 ofthe drawings wherein a demagnetizing coil in is arranged to be connectedto alternating current supply conductors ii and i2 through contactors I!and Nb. Now the novel method of the present invention includes theplacing of a part to be demagnetized (not shown) in the coil l0, turningthecurrent on and off in rapid succession to produce a plurality ofstarting transients (preferably at least ten or more) and thenwithdrawing the part from the coil during the time the coil is energizedby the steady flow of alternating current from the power supply lines.and I2. The control circuit for carrying out such a method includes asynchronous timer l5 which is connected through a dropping resistorifito the supply conductors II and the motor I1 is arranged to cause theswit h is to be opened after the elapse of a predetermine period oftime.

As soon as switch :18 is closed, will be observed that the motor isenergized through conductors ii and H8". The contacts and iilb in themain circuit are arranged to be closedupon ene1-= gization of acontactor coil which is connected through a normally closed contact 21'and switch it across'conductors ii and The normally closed contact willhereinafter be referred to as an interlock for this contact 28 isarranged to be opened as the contacts 09a and i319 are closed. It willthus be seen that as soon as the contacts 09a and 11% are closed, thecontac'tor coil 89 becomes deenergized by the coercing of the interlockill and the contacts i301 and i922 thereupon drop out. But as soon asthe contacts 119a and 8% drop out, the interlock so is closed and thecontactor coil 89 again becomes energized to cause the closing of thecontacts lilo and [l-Sb. This results in a rapid opening closing of theenergization circuit to the den-magnetizing coil ill.

Connected in shunt with the contactor coil iii and the interlock Bil isa timer coil 20 which is arranged to cause the movable contact element26a which is connected to one end of the contactor coil ill through aconductor 23 to move from its full line position as shown in Figure l toits dotted line position as shown in Figure 1, After the timer coil 2ihas caused the switch Zia to close, it will be observed the interlock isshmted out of effective control ofthe energizetion of the contactor coil09 and the contactor coil is will remain continuously energized untilthe synchronous timer 15 has caused the switch ill to open. During thislatter period the part which has been disposed within the demagnetizingcoil it is gradually withdrawn.

In any circuit, when first making contact, a transient current willnearly always occur because the relationship between the voltage andcurrent in that circuit at the particular instant of contact will not,in general, be the same as for the steady state condition. l ihenconsidering the demagnetizing coil id of Figure l by way of example, thesteady state condition would be represented by a sine wave 2 3 ofcurrent lagging 90 approximately behind the ap-.

plied voltage wave (as shown Figure 2). This 90 lag is of course due tothe fact that the resistance of the coil lb is negligible in comparisonwith the inductance. Now when the circuit to the demagnetizer coil i isclosed (by closure of contacts 09a and 8%) at a time "01, the current atthe instant of closing is zero, which obvi ously does not coincide withthe finite value of current "g which would be present that instant underthe steady state condition. As a result, a transient is establishedwhich makes up the difference in current and supplies the energyrequired to establish the held of the coil. The transient in the coil tohas the shape shown by the dotted curve 2t (an exponential curve) andhas a maximum value corresponding to the value My",

If an oscillogram is now taken of the line current starting at the timea, the picture would appear as shown by the full line curve ill inFigure 3. Figure 3 is derived by adding the steady state current to thetransient.

The effect can be analyzed by considering a D. C. transient to bepresent for the first live or six cycles in addition to the normalsteady state current. The magnitude oi. the transient will depend on theinstant at which the switch is closed.

' netized part.

The maximum transient will made at an instant of time 12 corresponds toa closing of the contact at an ln stant of timewhen the current waveshoul" be maximum in a positive direction (b) or in negative direction(0). It the circuit at a time y'f or in other words at a when thecurrent wave should be zero, there will of course be no transient atall. It will furthermore be observed from the above consideration thatthe transient may be either positive or negative, depending on the timeoi the closing.

Use may be made or this C. transient by causing it to oppose theoriginal field in the maglily energizing the coil a number of times itis believed a transient will always result of high magnitude which is inthe proper direction to neutralize a substantial part or the field inthe magnetized part or even to reverse it to some extent. From thispoint, the usual withdrawal of the part through the coil is sumcient toremove the remaining magnetism. Should another transient in the wrongdirection he applied, the beneficial efiect of the first tronsient isnot lost to any great extent. 'lhis has been conclusively proved inpractice. It is believed that an explanation of this efiect may beexplained by the hysteresis curve shown in Figure 4. The point 28represents the residual mam netism left in the part after the originalinsane tization. Point 29 represents the amount left after a favorabletransient. Point 3b shows how the residual magnetism is stillconsiderably less than that at 28 in spite of an unfavorable transientbeing applied after point 29. Point ill is arrived at by a furtherfavorable transient. Demagnetization from .point to will not be quite asgood as that from point but nevertheless it is still substantiallybetter than what it was at the point 28 where it originally started.

It has furthermore been found in practice that the beneficial effectobtained by rapidly interrupting'the energization circuit to themagnetizing coil to is due to the starting transient when the circuit ismade and not due to the condition which exists at the break. Numeroustests have further shown that a beneficial result is always obtained bya series of openings and closings of the energization circuit of thecoil iii A modified form of the present invention is shown in Figure 5ofthe drawings. In this embodiment the demagnetizing coil ill is alsoconnected to the power lines it and i2 through contactors lilo and i9?)as described in connection with Figure l. The parts are similar to thoseshown in Figure l and they have been given the same referencecharacters. A synchronous timer l5 having a motor l l and a timer switchill is also connected across the lines it and i2 through a droppingresist-or id. The contactor coil 58 in this instance, however, isconnected through a normally closed relay contact 32 and through theswitch it to the lines ii and i2 rather than through the mechanicalinterlock previously described. A timer microswitch Zia is providedwhich is normally open but which is arranged to be closed after a briefinterval of time by the timer coll 2| which is connected to the circuitin the same'manner as that described in connection with Figure 1. Arelay coil 33 is connected across the demagnetizin coil iii so that itis on the same side of the contactors E o and lob as is the demagnetizercoil ill. It will thus be apparent that upon closure of the contacts Naand 8% by energization of the contactor coil ID, the contacts its andI9?) drop out and the magnetizing coil to as well as the relay coil 33becomes deenergized. The cycle is rapidly repeated until the timermicroswitch 2 la has closed thus holding the contactor coil l9continually energized so long as the synchronous timer switch l8 remainsclosed. During this period the part is slowly withdrawn from thedemagnetizing coil l0. After the elapse or a predetermined interval oftime, the synchronous motor it opens the switch It and prevents furtherenergization of the magnetizing coil l until the switch 13 has againbeen closed.

A third embodiment of the present invention is illustrated in Figure 6of the drawings, wherein means is provided for obtaining a somewhatslower interruption of the contacts 130 and Nb. In this form of theinvention, the contactor coil i3 is connected through a microswitch 33and the switch it of the synchronous timer ll to the lines it and II.The microswitch 35a i controlled by a timer coil 35 which is connectedthrough a mechanical interlock 36 and a microswitch 38a across the linesI I and I2. The microswitch 38a is operated by the timer coil 33 whichis connected across the lines H and I2 through switch is or thesynchronous timer ii. The synchronous timer I5 is connected across the,lines II and 12 through a. dropping resistor It in the same manner aspreviously described.

When the synchronous timer I5 is turned on by closing its switch I8, thecontactor coil l3 and timer coil 38 are energized. The energization ofthe contactor i9 causes the contacts I31: and Nb to be closed toenergize. the magnetizing coil ill. The interlock 38 is mechanicallyconnected to the contactors Na, and l9b in such a manner that uponclosure of the latter, the interlock 33 closes. When the interlock 38closes, the timer coil 35 is energized and after theelapse of apredetermined period of time, such for example as twotenths of a second,the microswitch 33a opens after opening the energization circuit of thecontactor coil is. Deenergization of the contactor coil l9 causes thecontacts Isa and Nb to drop out and results in the deenergization of thedemagnetizing coil ID. The opening of the contacts 18a and 19b causesthe cycle to repeat itself at twotenths second intervals. After theelapse of a predetermined period of time, such for example as twoseconds (or in other words twenty twotenths second intervals) the timer38 causes its microswitch 38a to disconnect timer 35 from the circuit.This stops the intermittent action and causes the demagnetizer coil toremain energized until the synchronous timer shuts off the entirecircuit.

It is evident that with this particular embodiment of the presentinvention, the rate at which the transients are produced, and the numberof transients which occur before a steady operation is reached, are bothcontrollable through the timers 33 and 38.

In practice it has been found that a circuit of the general type shownin Figure 6 is more uniform in satisfactory results, for it has beenfound that ii the duration of a transient is very short, it is not aseffective in its demagnetizing action as where the duration of thetransient is somewhat longer. I have found that under usual operatingconditions, the minimum length of time is about six cycles (Where sixtycycle alternatin current is used) or one-tenth of a second. It hasfurther been found in practice that the efiectivenessof thedemagnetization increases with the number of transients used butpractically the entire benefit of the process is obtained with ten tofifteen transients.

' While I have shown and described certain particular embodiments of myinvention, 'it will, of course, be understood that I do not wish to belimited thereto, since many modifications may be made, and I, therefore,contemplate by the appended claims to cover all such modifications asfall within the true spirit and scope of my invention.

I claim as my invention:

1. Demagnetization apparatus comprising a demagnetizing coil in which amagnetized part is placed when it is to be demagnetized, means forenergizing said coil with a series of A. C. starting transients for apredetermined period of time, and means for energizing said coil with asteady state A. C. after said predetermined period of energization.

2. Demagnetizationapparatus comprising a demagnetizing coil, means forintroducing in rapid succession a series of alternating currenttransients insaid coil for a predetermined period of time, and means forcausing an alternating current of substantially constant maximumamplitud to flow through said coil after the elapse of saidpredetermined period of time.

3. Demagnetization apparatus comprising a demagnetizing coil, means forenergizing said coil with a plurality of A. C. starting transients inrapid succession, and means for thereafter energizing said coil withalternating current of susbtantially uniform amplitude.

4. Demagnetization apparatus comprising a demagnetizing coil, means forenergizing said coil with a series of A. C. starting transients for apredetermined period of time, and means for energizing said coil withalternating current of substantially uniform amplitude for a secondpredetermined period of time immediately following said first period oftime.

5. Demagnetization apparatus comprising a demagnetizing coil. means forenergizing said coil with a successively applied group of A. C. startingtransients, each transient being applied for a few cycles only, andmeans for thereafter energizing said coil with alternating current ofsubstantially constant amplitude.

6. Demagnetization apparatus comprising a demagnetizing coil, means forenergizing said coil with alternating current of substantial constantamplitude, and means for initially peaking the amplitude of thealternating current wave for a predetermined period of time.

7. A circuit for controlling the energization of a demagnetizercomprising supply conductors arranged to be connected to a source ofalternating current, a demagnetizer including a circuit esswitch afterthe elapse of a of time.

8. A circuit for controlling the energization of a demagnetizercomprising supply conductors arranged-to be connected to a source ofalternating current, a demagnetizer, means for connecting saiddemagnetizer to said supply conductors including a contactor having acontactor operating coil, and a contact interlock which opens when thecontactor closes and which closes when the contactor opens, asynchronous timer connected to said supply conductors and having asynchronous timer switch which opens after the elapse of a predeterminedperiod of time, said contactor coil and said interlock being connectedin series with said synchronous timer switch, a microtimer switchconnected in parallel with said interlock, said microtimer switch havinga timer coil for closing said switch after a predetermined period oftime, the predetermined period of time of said microtimer switch beingshorter than the predetermined period of time of said synchronous timer.

9. A circuit for controlling the energization of a demagnetizercomprising supply conductors arranged to be connected to a source ofalternating current, a demagnetizer, means for connecting saiddemagnetizer to said supply conductors including a contactor havingnormally open contacts and a contact operating coil which closes thecontacts upon energization thereof, a normally closedrelay switch, arelay coil for opening said relay switch upon energization of said relaycoil, said relay coil being connected in parallel with said demagnetizerand on the normally open side of said contacts, and means for conmeetingsaid contact operating coil and said relay switch in series to saidsupply conductors.

10. A circuit for controlling the energization of a demagnetizercomprising supply conductors arranged to be connected to a source ofalternating current, a demagnctizer, means for connecting saiddemagnetizer to said supply conductors including a contactor havingnormally open contacts and a contact operating coil which closes thecontacts upon energization thereof, a normally closed relay switch, arelay coil for opening said relay switch upon energization thereof, amicrbtimer having a normally closed microtlmer switch and a timer coilwhich opens said microtimer switch after the elapse of a predeterminedperiod of .energization of said timer coil, said relay coil beingconnected in parallel with said demagnetizer and on the normally openside of said contactor, said contactor coil and said relay switch beingconnected in series across said supply conductors, said timer coil beingconnected across said supply conductors, and said timer microswitchbeing connected in parallel to said relay switch.

11. A circuit for controlling the energization of a demagnetizercomprising supply conductors arranged to be connected to a source ofalternating current. a demagnetizer, means for connecting saiddemagnetizer to said supplysconpredetermined period ductors including acontactor having normally open contacts, and a contact operating coilwhich closes the contacts upon energization thereof, a normally closedrelay switch, a relay coil for opening said relay switch uponenergization thereof. said relay coil being connected in parallel withsaid demagnetizer and on the normally open side of said contactor, amicrotimer including a normally open microtlmer switch and a timer coilfor closing said switch a predeteracorns? mined period of time after theenerglzation of said timer coil, and a synchronous timer having a timermotor and a synchronous timer switch which is opened by said motor afterthe elapse of a predetermined period of time, said last period of timebeing greater than the period of time for closing said microtimerswitch, said contactor coil and said relay switch being connected inseries through said synchronous timer switch, said microtimer switchbeing connected in pare allel with said relay switch and said microtimercoil being connected through said synchronous timer switch to saidsupply conductors.

12. A circuit for controlling the energization of a demagnetizercomprising supply conductors arranged to he connecmd to a source ofalternating current, a demagnetizer, means for connecting saiddemagnetizer to said supply conductors including a contacto-r havingnormally open contacts, and a contact operating coil which closes thecontacts upon energization thereof, a first microtimer having a timercoil and a normally closed microtimer switch, a second microtinierhaving a timer coil and a normally closed microtimer switch, aninterlock switch on said contactor arranged to close when the contactsof said contactor are closed and to open when the contacts of saidcontactor are open, said contactor coil and said first microswitch beingconnected in series to said supply conductors, said first microtimercoil, said interlock switch and said second microswitch being connectedin series to said supply conductors, said second microtimcr coil heingconnected to said supply conductors, said first microtimer coil beingarranged to open its associated microswitch after the elapse of apredetermined period of time, and said second microtimer coil beingarranged to open its associated switch af ter the elapse or" apredetermined period of time which is greater than the predeterminedperiod of time for said first microtimer. I

13. A circuit for controlling the energization of a demagnetizercomprising supply conductors rs mg current, a demagnetizer, means forconnecting said demagnetizer to said supply conductors including acontactor having normally open contacts, and a contact operating coilwhich closes the contacts upon energization thereof, a first mi- 00crotimer having a timer coil and a normally closed microtimer switch, asecond mlcrotimer having a timer coil and a normally closed microtimerswitch, said first microtimer coil being arranged to open its associatedmicroswitch after the elapse of a predetermined period of time, saidsecond microtimer coil being arranged to open its associated microswitchafter the elapse of a predetermined period of time greater than thepredetermined period of time of said first microtimer, a synchronoustimer having a motor and a closable switch which is arranged to beopened a predetermined period of time after the closure thereof, saidlast mentioned predetermined period of time being greater than thepredetermined period of time of said second microtimer, said contactorcoil and said first microswitch being connected through said synchronoustimer switch across said supply conductors, an interlock switch arrangedto open and close with the contacts of 70 said contactor, said firsttimer coil, said interlock switch and said second microswitch beingconnected in series across said supply conductors, and said second timercoil being connected through said synchronous timer switch across said 7supply conductors.

arranged to be connected to a source of a-lternatwenew 14. The method ofeleetricagly demegnetizing magnetized parts which includes subjectingthe part to the magnetic infiveme e2 magnetic fields preduced byeltemeting 0 event transients and then slewly withdrawing the peri; froma steady altemetimg magnetyie fl a megneisizeai per: whicl'a incfiudeesubjecting fihe part 50 e, termpted series of magnetic fields gorndueeeseries of alternating current starting and then slowly withdrawing theper; magnetic field produced by a steady e5 netzlng current.

